The present invention relates to an apparatus for converting the kinetic energy in a bunched electron beam into radio frequency (RF) energy and distributing the RF energy to multiple waveguides.
Practitioners have produced high power (multi-gigawatt) RF generators that convert an Intense Relativistic Electron Beam (IREB) into RF energy. U.S. Pat. No. 3,354,348 issued to Van Iperen discloses a generator that directs an electron beam into a resonant cavity. U.S. Pat. No. 4,345,220 issued to Sullivan discloses a virtual cathode generator that produces transverse magnetic (TM) waves, which propagate through a hollow waveguide towards an output horn.
Practitioners have produced high-power RF energy by directing an IREB upon the center conductor of a coaxial waveguide structure, as discussed in Friedman et al., Operation of a Multigigawatt Relativistic Klystron Amplifier, SPIE, vol. 1061, pp. 34-47, 1989, and Friedman et al., Generation of a High-Power RF Pulse in a Rectangular Waveguide, Rev. Sci. Instrum., vol. 58, pp. 58-59, January 1987. The excitation of the center conductor by the IREB launches transverse electric and magnetic (TEM) waves. In the electron beam converters disclosed by Friedman et al., the TEM waves propagate along the coaxial structure toward a horn, where they are radiated.
However, such high power converters cannot efficiently be used to feed radar antennas because they could produce more power than a typical waveguide can extract. The maximum power that a waveguide can transmit is limited by the voltage breakdown capabilities of the metallic walls of the waveguide in a vacuum. This maximum power can be calculated using well-known formulas and may be about 60 megawatts (MW) for a standard WR-137 waveguide containing a signal having a maximum electric field of 1.5.times.10.sup.7 V/m at a frequency of 6 gigahertz (GHz). Thus, multi-gigawatt electron beam converters, such as those disclosed by Friedman et al., typically comprise a horn for radiating the RF energy almost immediately after conversion and are not connected to standard waveguides. The power that can be extracted from such electron beam converters is further described in Buschauer, RF Power Calculations for the NRL Buncher/Converter Microwave Generator, Rev. Sci. Instrum., vol. 60., pp. 752-753, April 1989.
Antenna arrays, such as those in phased-array radar systems, commonly have multiple RF inputs. The inputs may receive RF energy distributed through a branching waveguide arrangement connected to a single conventional RF generator, such as low-power klystron. A branching waveguide arrangement is disclosed in U.S. Pat. No. 2,445,895 issued to Tyrell. However, the relatively low power produced by conventional RF generators limits their use to feeding single antennas or small antenna arrays.
It would be desirable to generate high power RF energy and efficiently distribute it among multiple waveguides, which could feed large antenna arrays. These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.